In code division multiple access (CDMA) communication systems, multiple communications may be simultaneously sent over a shared frequency spectrum. Each communication is distinguished by the code used to transmit the communication. Data symbols of a communication are spread using chips of the code. The number of chips used to transmit a particular symbol is referred to as the spreading factor. One common spreading factor is sixteen (16), where sixteen chips are used to transmit one symbol. By way of example, typical spreading factors (SF) are 16, 8, 4, 2 and 1 in TDD/CDMA communication systems.
In some CDMA communication systems, to better utilize the shared spectrum, the spectrum is time divided into frames having a predetermined number of time slots, such as fifteen time slots. This type of system is referred to as a hybrid CDMA/time division multiple access (TDMA) communication system. One such system, which restricts uplink communications and downlink communications to particular time slots, is a time division duplex communication (TDD) system.
One approach to receive the multiple communications transmitted within the shared spectrum is joint detection. In joint detection, the data from the multiple communications is determined together. The joint detector uses the, known or determined, codes of the multiple communications and estimates the data of the multiple communications as soft symbols. Some typical implementations for joint detectors use zero forcing block linear equalizers (ZF-BLE), Cholesky or approximate Cholesky decomposition or fast Fourier transforms.
Communications are received by a receiver at a particular spreading factor. The higher spreading factor at which communications are received, the more complicated it is to perform joint detection. It is therefore desirable to provide a method and apparatus to reduce the complexity of performing joint detection in wireless communication systems.